This description relates to a half wave expulsion-(non-fault current limiting) type superconducting fault current limiter having an integral high speed switch module.
Current limiters and circuit breakers in an electric power system are applied to prevent an over-current more than a threshold value generated by accidents such as thunder-stroke, earth fault, short circuit, etc from flowing into the system.
Of all the current limiters, FCLs (Fault Current Limiters), which use superconducting elements, supply an electric power supplied from a power feeder to a system without loss due to unique characteristic of the superconducting elements, and restrict an over-current more than a threshold value generated by accidents such as thunder-stroke, earth fault, short circuit, etc.
Thus, the FCLs restrict a mechanical, thermal and electrical stress caused by electric power appliances such as a bus-bar, an insulator and a circuit breaker, etc.
On the other hand, a circuit breaker connected to an electric power system detects an over-current more than a threshold value, breaks the connection with the system in accordance with control of an over-current relay generating a breaking signal and thus prevents the over-current from flowing into the system.
Hereinafter, an FCL in accordance with related art will be described in detail with reference to accompanying drawings. FIG. 1 shows a connected state of superconducting elements in accordance with an electric power capacity in superconducting fault-current limiters, and FIG. 2 shows a detailed part of FIG. 1.
Referring to FIG. 1, the conventional FCL includes a trigger matrix 100A for generating and supplying a magnetic field in order to induce concurrent quench of superconducting elements corresponding to a series connection of each row in case of generation of an over-current more than a threshold value caused by accidents such as thunder-stroke, earth fault, short circuit, a current limit matrix 100B for restricting the over-current more than the threshold value generated by accidents such as thunder-stroke, earth fault, short circuit, etc
As shown in FIG. 2, the trigger matrix 100A comprises n number of trigger matrix elements 110-1 through 110-n formed in accordance with current capacity required by an electric power system, wherein the respective trigger matrix elements include a superconducting element RR1, a coil LL1 surrounding the superconducting elements RR1.
As in FIG. 2, the current limit matrix 100B comprises n number of current limit matrix elements 114-1 through 114-n connected to the trigger matrix element 110-1, wherein the respective current limit elements include a superconducting element RR1, a coil LL1 surrounding the superconducting elements RR1 and a coil LL1 connected in parallel to the coil LL1. In addition, the current limit matrix 100B is serially connected to m number of current limit modules (Module 112-1 through 112-m), wherein the respective current limit modules are n number of the current limit matrix elements 114-1 through 114-n. 
Therefore, in FCLs applied to an electric power system, n number of the trigger matrix elements 110-1 through 110-n formed in accordance with a current capacity required by an electric power system are connected to n number of the current limit matrix elements 114-1 through 114-n connected to n number of the trigger matrix elements 110-1, n number of the current limit matrix elements 114-1 through 114-n become respectively current limit modules (Module 112-1 through 112-m) and m number of the current limit modules (Module 112-1 through 112-m) are serially connected in accordance with a voltage capacity required in an electric power system. That is, superconducting elements included in a trigger matrix element and a current limit matrix element are serially and in parallel connected in accordance with the current capacity required in the electric power system.
As in FIG. 2 showing a detailed part of FIG. 1, the superconducting element RR1 and the trigger matrix element 110-1 of the coil LL1 surrounding the superconducting elements RR1 are connected to an electric power line that receives an electric power from a power feeder 100. The current limit matrix elements 114-1 include the superconducting element RR1, a coil L11 surrounding the superconducting elements RR1 and a coil LL11 connected in parallel to the superconducting element RR1, a coil L11 surrounding the superconducting elements RR1, and m number of the current limit matrix elements 114-1 through 114-m are serially respectively connected in accordance with a voltage capacity. The trigger matrix element 110-1 is connected in parallel to m number of the current limit matrix elements 114-1 through 114-m in accordance with a current capacity required by an electric power system.
Referring to FIG. 2, superconducting elements (RR1, R11, R21, . . . Rm1) supply an electric power supplied from a power feeder to a system without loss of the electric power in a case that a stationary current flows thereinto. In case of the stationary current, inductance elements generated in coils (LL1, LL11, LL21 . . . LLm1) surrounding respective superconducting elements are offset.
On the other hand, when an over current more than a threshold value generated by accidents such as thunder-stroke, earth fault, short circuit, etc, the superconducting element RR1 generates a high resistance value, being quenched in a phase transition state.
The over current flows into the coil LL1 surrounding the superconducting element RR1 by the generated resistance value and thus a magnetic field is generated. Herein, this magnetic field is simultaneously supplied to coils LL11 through LLm1 serially connected. A high resistance value is generated in a case that the superconducting elements R11 through Rm1 are quenched by the magnetic field and thus the superconducting elements R11 through Rm1 distribute the over current into the coils L11 through Lm1 connected in parallel to the superconducting elements R11 through Rm1. In conclusion, the superconducting elements R11 through Rm1 are not destroyed by the over-current, such that the over-current is restricted by an impedance value included in the coils L11 through Lm1 to block an influx of the over-current into a system 150.
For the operation thus described, respective superconducting elements should be manufactured to have the same characteristic and cooled by being surrounded by refrigerants such as liquid nitrogen, etc.
As described above, superconducting elements of the FCLs are transmitted to a phase transition state by an over-current or a temperature more than a threshold value, whereby a high resistance is generated to restrict the over-current. In addition, the superconducting elements of the FCLs are restored to a superconducting state by being cooled to a temperature of superconducting state through a cooling device.
However, the superconducting elements of FCLs suffer from drawbacks in that the elements have a low acceptable electric power capacity per unit length, and thus serial and parallel connections are required for being applied to an electric power system, and an increase in serial and parallel connections of superconducting elements by geometric progression is required in a high voltage electric power system. As such being the case, the increase of connection points in accordance with serial and parallel connections of superconducting elements causes instability of FCLs, thereby disabling a safe electric power to be supplied to the electric power system. Another drawback is that the FCLs cannot be applied to a real electric power system because of a high manufacturing cost and a complicated technique for the serial and parallel connections of superconducting elements. Still another drawback is that cooling costs and techniques for maintaining a superconducting state of FCLs bar an actual application to the electric system.
There may still be further drawback in that, because a considerable time is required for restoration from a phase transition to a superconducting state, a re-closing circuit condition required in a general electric power system within a second is difficult to be satisfied.
Meanwhile, whereas 3 to 5 periods are required in a circuit breaker for breaking an over-current more than a threshold value in response to a control of an over-current relay, the FCLs restricts the over-current upon detection of the over-current which is more than the threshold value according to a unique characteristic of superconducting elements. The over-current relay detects an over-current exceeding a threshold value and transmits a cut-off signal to a breaker, but if the FCLS restricts the over-current before the over-current relay detects the over-current, the over-current relay cannot normally operate and control the breaker.